Various types of equipment exist for semiconductor processing such as plasma etching, ion implantation, sputtering, rapid thermal processing (RTP), photolithography, chemical vapor deposition (CVD), and flat panel display fabrication processes wherein etching, resist stripping, passivation, deposition, and the like, are carried out. For example, a vacuum processing chamber may be used for etching and chemical vapor deposition of materials on substrates by supplying an etching or deposition gas to the vacuum chamber and application of radio frequencey (RF) energy to the gas. Electromagnetic coupling of RF energy into the source region of a vacuum chamber is conventionally employed to generate and maintain a high electron density plasma having a low particle energy.
Plasma generation is used in a variety of such semiconductor fabrication processes. Plasma generating equipment includes parallel plate reactors such as the type disclosed in commonly owned U.S. Pat. No. 4,340,462, electron cyclotron resonance (ECR) systems such as the type disclosed in commonly owned U.S. Pat. No. 5,200,232, and transformer or inductively coupled plasma (TCP/ICP) systems such as the type disclosed in commonly owned U.S. Pat. No. 4,948,458.
In addition to the RF source which generates the plasma, RF bias energy may be capacitively coupled to the plasma via the article being processed to increase and control the energy of ions impinging on the article. The RF bias power may be capacitively coupled to the plasma via the wafer and chuck. Typically, plasma density is controlled by the RF source power, and ion energy is independently controlled by the RF bias power. To provide the requisite RF fields in the vacuum chamber, the RF source and RF bias generally operate at high voltages.
The high voltage of the RF bias is typically applied to the plasma through an electrode cap in the vacuum processing chamber. Because the cap is powered with a high RF voltage with respect to the electrode housing in the vacuum processing chamber, arcing is likely to occur if there is insufficient spacing between the cap and the grounded housing. Thus, vacuum processing chambers typically include a ceramic insulator plate disposed between the high RF voltage electrode cap and the electrode housing which is at ground potential. The ceramic insulator plate provides the adequate spacing between the electrode cap and the grounded housing to prevent arcing.
A typical method of securing the ceramic insulating plate to the electrode cap is shown in FIG. 1. The method involves threading a hole 10 partway through the ceramic plate 20 (a "blind" hole) and attaching the electrode cap 30 with a screw 40 which is threaded into the blind hole 10. While this method may perform satisfactorily under most conditions, problems can arise, for example, when the ceramic insulator plate 20 is subject to different heating conditions. An uneven heat distribution in the ceramic insulator plate 20 may produce uncontrolled torquing and cause mechanical stresses to develop in the ceramic, with the result that the threads of the blind hole 10 in the ceramic are damaged. Ceramics have a low tolerance for bending moments, which may develop in the threads of the blind hole due to the temperature variations. If even one thread is damaged, the entire ceramic insulating plate, which may include other expensive components, must be replaced.